1. Field of the Invention
This invention relates to an apparatus for ophthalmologic examination for effecting the measurement of the velocity of blood current in the fundus of an eye.
2. Related Background Art
FIG. 1 of the accompanying drawings shows a prior-art example of an eye fundus blood current meter which is one of apparatuses for ophthalmologic examination and in which a slip lamp generally used for ophthalmologic diagnosis and treatment has been reconstructed. The principle of blood current measurement will hereinafter be described by the use of this prior-art example. An illuminating optical system is disposed on an optical path K1, and a beam of white light from an illuminating light source 1 is reflected by an apertured mirror 2 and illuminates a blood vessel Ev on the fundus Ea of an eye through a slit 3, a lens 4 and a contact lens 5 which offsets the refractive power of the cornea of an eye E to be examined and enables the observation of the fundus Ea of the eye. Also, a measuring laser source 6 emitting an He-Ne laser beam for measurement is disposed on an optical path behind the apertured mirror 2, and the measuring light from the measuring laser source 6 passes through the central opening portion of the apertured mirror 2 and is made coaxial with the beam of light from the illuminating light source 1 and illuminates the fundus Ea of the eye in a spot-like shape through the slit 3, the lens 4 and the contact lens 5.
A beam of light scatteringly reflected by blood corpuscles flowing through the blood vessel Ev and the wall of the blood vessel passes through the objective lenses 7a and 7b of a light receiving optical system for stereoscopic observation disposed on optical paths K2 and K3 forming an angle .alpha.' therebetween, is reflected by mirrors 8a, 8b and mirrors 9a, 9b and are observed as the image of the fundus of the eye by an examiner through eyepieces 10a, 10b, and the examiner selects a measured area while looking into the eyepieces 10a, 10b and observing the fundus Ea of the eye.
FIG. 2 shows the image of the fundus of the eye observed by the examiner. When in an area I being illuminated by the illuminating light, the blood vessel Ev to be measured is aligned with a scale SC prepared in advance on the focal planes of the eyepieces 10a, 10b, the measuring light from the measuring laser source 6 and the blood vessel Ev are aligned with each other, and the measured area is determined by a spot light beam PS from the measuring laser source 6. At this time, the beam of reflected light of the measuring light reflected by the fundus Ea of the eye is received by photo-multipliers 12a, 12b through optical fibers 11a, 11b.
These received light signals include a predetermined beat signal component created by a component Doppler-shifted by the blood current flowing through the blood vessel Ev and a component reflected by the stationary wall of the blood vessel interfering with each other, and this beat signal is frequency-analyzed to thereby find the velocity of the blood current in the blood vessel Ev.
FIG. 3 of the accompanying drawings shows an example of the result of the frequency analysis of the received light signals measured by the photo-multipliers 12a, 12b, and the axis of abscissas indicates a frequency .DELTA.f and the axis of ordinates indicates the output .DELTA.s thereof. The relation among the maximum shift .DELTA.fmax of the frequency, the wave number vector .kappa.i of the incident beam of light, the wave number vector .kappa.s of the received beam of light and the velocity vector .nu. of the blood current can be expressed as EQU .DELTA.fmax=(.kappa.s-.kappa.i).multidot.V (1)
Accordingly, when expression (1) is modified by the use of the maximum shifts .DELTA.fmax1 and .DELTA.fmax2 of the frequency calculated from the received light signals of the photo-multipliers 12a and 12b, the wavelength .lambda. of the laser beam, the refractive index n of the measured area, the angle a formed by light receiving optical axes k2 and k3 in the eye and the angle .beta. formed by light receiving optical axes k2 and k3 in the eye, the maximum velocity Vmax of the blood current can be expressed as EQU Vmax={.lambda./(n.alpha.)}.multidot..vertline..DELTA.fmax1-.DELTA.fmax2.ver tline./cos.beta. (2)
By thus effecting measurement from two directions, the contribution of the measuring light in the direction of incidence thereof is offset and the blood current in any area on the fundus Ea of the eye can be measured.
Also, to measure the true velocity of the blood current from the relation between the line of intersection A between a plane formed by the two light receiving optical paths k2 and k3 and the fundus Ea of the eye and the angle .beta. formed by the line of intersection A and the velocity vector .nu. of the blood current, it is necessary to make this line of intersection A coincident with the velocity vector .nu., with .beta.=0.degree. in expression (2). Therefore, in the example of the prior art, the entire light receiving optical system is rotated or an image rotator is disposed in the light receiving optical system so that the line of intersection A may be made optically coincident with the velocity vector .nu..
Blood current measurement data recorded by such an apparatus, according to the prior art, are shown in FIG. 4 of the accompanying drawings. Heretofore, the recording of measurement data has been started simultaneously with measurement start Ts and therefore, the phase of the top of the data has been quite random and the comparison thereof with other data has sometimes been difficult. Also, the end Te of data recording has been set by a measurement time Tm and therefore, in which phase of pulsation the data terminates has not been determined, and there has been the possibility that when parameters such as the average flow velocity, the number of pulsations and the maximum and minimum values per pulsation are to be calculated from recorded data, an error is included, depending on the phase of pulsation.
Also, there has heretofore been no apparatus for appropriately measuring a variation in the amount of blood current with time.
Further, there has been desired an apparatus for displaying the result of the measurement of such a state of blood current so that the examiner can appropriately judge it.